American Express is upgrading its Sync program with Twitter to let cardholders buy stuff by using a hashtag. Starting Monday, AmEx customers who sync their cards can buy items if they use the right hashtag. The first such item is a $25 AmEx gift card, which will go for $15 if you tweet #BuyAmexGiftCard25. Other offers will be rolled out on Wednesday Feb. 13 at noon EST including an Amazon Kindle Fire HD for $149.99 (a $50 discount), an Xbox Controller for $29.99 (a discount of about $10) and an Xbox 360 4GB console with a three-month Xbox LIVE Subscription and two game tokens for $179.99 (which is the price of the console without those extras.) If consumers opt for those items and use the correct hashtags, then they will get a verification from @AmexSync, which will contain a confirmation hashtag. Cardholders then have 15 minutes to tweet the confirmation hashtag to confirm their purchase.